1. Field of the Invention
The present invention relates to a potential measuring device which measures a surface potential of a charged object in a non-contact manner.
2. Description of the Related Art
Various types of devices have been developed as a potential measuring device which measures a surface potential in a non-contact manner For example, a surface potential sensor (see Patent Document 1) is known. A piezoelectric driving element is used for driving this surface potential sensor. In Patent Document 2, a linear actuator is described as a structure for driving a driven region. In structures driving driven parts using a coil, which are described in these Patent Document 1 and Patent Document 2, a magnet (permanent magnet) and a back yoke are provided in a state of opposing a coil (electromagnet) on one end side of the coil. Thus, when an electric current is conducted through the coil, it is possible to drive a driver in a direction orthogonal to a lining direction of the coil and the magnet.
[Patent Document 1] Japanese Patent Application Laid-open No. H10-115647
[Patent Document 2] Japanese Patent Application Laid-open No. 2010-166685
However, in the potential measuring device of Patent Document 1, a vibrating piece vibrates in a direction (width direction) orthogonal to its extending direction, and thus a displacement amount of the vibrating piece is small. Further, in the structure described in Patent Document 2, the magnet and the back yoke are disposed only on one end side of the coil. Thus, magnetic efficiency thereof is not good, and therefore a driving force obtained by a magnetic force generated in the coil is weak.
The subject matter of the present application is made in view of the above-described situation, and at least an embodiment provides a potential measuring device of non-contact type having better magnetic efficiency than conventional potential measuring devices.